The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component that can be created using a fabrication process) has decreased. In correlation with the decrease of geometry size, spacing between various devices on a chip has also shrunk. For example, spacing between metal interconnect lines, known as interconnect spacing size, has been shrinking with each new generation of semiconductor fabrication technology.
Meanwhile, vias are used to provide electrical connections between metal layers. As the interconnect spacing size decreases, it is difficult to produce a via that aligns perfectly with the desired metal interconnect. The lack of perfect alignment may be referred to as an overlay error. If the overlay error becomes great enough, undesired bridging between vias coupled to respective metal interconnect lines on the same metal layer may occur, which causes an electrical short defect. This defect may also be referred to as a via-induced-metal-bridge (VIMB) defect. The VIMB defect is further exacerbated if via sizes are big relative to widths of metal interconnect lines or interconnect spacing sizes. In addition, a time dependent dielectric breakdown (TDDB) problem gets worse as spacing sizes shrink. Current methods of forming vias have difficulties in overcoming these problems mentioned above. Therefore, while existing methods of forming vias have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.